For a liquid crystal display apparatus including a liquid crystal panel that modulates the light source light according to a video signal, and a backlight light source to illuminate the liquid crystal panel, a technique is known according to which the quality level of the displayed video is improved by controlling the light emission luminance of the backlight light source corresponding to an input video signal.
For example, Patent Document 1 discloses a liquid crystal display apparatus that calculates the average picture level (hereinafter, referred to as “APL”) in one frame as a feature amount of an input video signal and adjusts the light emission luminance of the backlight light source corresponding to the APL.
However, when the light emission luminance is adjusted simply corresponding to the APL, for multi-screen display displaying both of a dark video and a bright video, the light emission luminance becomes the one that corresponds to an intermediate APL between the APL of the dark video and the APL of the bright video, and therefore, the feeling of brightness and the contrast feeling become unnatural.
For two-screen display displaying a video for a personal computer and a television video, when the light emission luminance control for the backlight light source of the overall two screens is executed corresponding to the APL of the television video, the light emission luminance is properly controlled for the screen displaying the television video while the light emission luminance is improper for the screen displaying the video for the personal computer, and the feeling of brightness and the contrast feeling thereof are unnatural.
Therefore, Patent Document 1 discloses a liquid crystal display apparatus that adjusts the light emission luminance of the backlight light, source corresponding to the APL but that discontinues the process of adjusting the light emission luminance corresponding to the APL of the input video signal when the multi-screen display is executed.
Patent Document 2 discloses an image display apparatus that, for executing two-screen display, properly improves the visual contrast feeling avoiding any uncomfortable feeling from both of the screens by correcting the amplitude of the video signal such that contrast adjustment and light source luminance adjustment are executed for the screen to be controlled and the effect of the light source luminance adjustment is cancelled for the screen not to be controlled.